Fair Value - Partnership's Financial Assets and Liabilities at Fair Value (Detail) - USD ($) $ in Millions		Mar. 29, 2024	Dec. 31, 2023	Mar. 31, 2023
Cash equivalents:
Total cash equivalents		$ 166	$ 255
Investments segregated under federal regulations:
Total investments segregated under federal regulations		11,516	11,393
Total investments segregated under federal regulations		11,516		$ 11,067
Investment securities:
Total investment securities		1,055	1,069
Inventory securities:
Total inventory securities		121	88
Other Assets:
Client Fractional Shares Ownership Assets		891	824
Accounts payable, accrued expenses and other:
Client Fractional Shares Redemption Obligations		891	824
Equities [Member]
Investment securities:
Total investment securities		12	11
Inventory securities:
Total inventory securities		67	21
Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		10	5
Government and Agency Obligations [Member]
Investment securities:
Total investment securities		591	600
Inventory securities:
Total inventory securities		3	4
U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		10,116	9,893
Mutual Funds [Member]
Investment securities:
Total investment securities	[1]	340	346
Inventory securities:
Total inventory securities		2	9
Municipal Obligations [Member]
Investment securities:
Total investment securities		12	12
Inventory securities:
Total inventory securities		36	29
Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		144	179
Investments segregated under federal regulations:
Total investments segregated under federal regulations		1,400	1,500
Investment securities:
Total investment securities		100	100
Inventory securities:
Total inventory securities		3	20
Money Market Funds [Member]
Cash equivalents:
Total cash equivalents		22	76
Level I [Member]
Cash equivalents:
Total cash equivalents		22	76
Investments segregated under federal regulations:
Total investments segregated under federal regulations		10,116	9,893
Investment securities:
Total investment securities		943	957
Inventory securities:
Total inventory securities		72	34
Other Assets:
Client Fractional Shares Ownership Assets		891	824
Accounts payable, accrued expenses and other:
Client Fractional Shares Redemption Obligations		891	824
Level I [Member] | Equities [Member]
Investment securities:
Total investment securities		12	11
Inventory securities:
Total inventory securities		67	21
Level I [Member] | Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		0	0
Level I [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment securities		591	600
Inventory securities:
Total inventory securities		3	4
Level I [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		10,116	9,893
Level I [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	[1]	340	346
Inventory securities:
Total inventory securities		2	9
Level I [Member] | Municipal Obligations [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level I [Member] | Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		0	0
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level I [Member] | Money Market Funds [Member]
Cash equivalents:
Total cash equivalents		22	76
Level II [Member]
Cash equivalents:
Total cash equivalents		144	179
Investments segregated under federal regulations:
Total investments segregated under federal regulations		1,400	1,500
Investment securities:
Total investment securities		112	112
Inventory securities:
Total inventory securities		49	54
Other Assets:
Client Fractional Shares Ownership Assets		0	0
Accounts payable, accrued expenses and other:
Client Fractional Shares Redemption Obligations		0	0
Level II [Member] | Equities [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level II [Member] | Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		10	5
Level II [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level II [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Level II [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	[1]	0	0
Inventory securities:
Total inventory securities		0	0
Level II [Member] | Municipal Obligations [Member]
Investment securities:
Total investment securities		12	12
Inventory securities:
Total inventory securities		36	29
Level II [Member] | Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		144	179
Investments segregated under federal regulations:
Total investments segregated under federal regulations		1,400	1,500
Investment securities:
Total investment securities		100	100
Inventory securities:
Total inventory securities		3	20
Level II [Member] | Money Market Funds [Member]
Cash equivalents:
Total cash equivalents		0	0
Level III [Member]
Cash equivalents:
Total cash equivalents		0	0
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Other Assets:
Client Fractional Shares Ownership Assets		0	0
Accounts payable, accrued expenses and other:
Client Fractional Shares Redemption Obligations		0	0
Level III [Member] | Equities [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Level III [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	[1]	0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Municipal Obligations [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		0	0
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Money Market Funds [Member]
Cash equivalents:
Total cash equivalents		$ 0	$ 0

[1] (1) The mutual funds balance consists primarily of securities held to economically hedge future liabilities for the non-qualified deferred compensation plan. The balance also includes a security held for regulatory purposes at the Trust Co.